Low-Frequency Oceanographic Variability Near Flemish Cap and Sackville Spur
Document Type Article
To address a need for science-based advice on issues of resource exploration, two oceanographic moorings were placed on the abyssal slope of northwest Flemish Cap from July 2013 to July 2014. These yielded some of the first long-term moored measurements of velocity, temperature, and salinity in the region. Hydrographic and lowered-ADCP measurements made during mooring deployment and recovery reveal that the deep Labrador Current flows approximately along isobaths between water depths of 1,200 and 2,200 m. However, these snapshots differ significantly, with stronger currents observed during the deployment survey. The mooring data, obtained near the 1,500 m isobath, reveal a complex temporal variation of the current. The velocity spectrum is dominated by a peak at a period of approximately 21 days, with power increasing with depth in the water column and varying through the year. In other boundary-current studies, variations in the several-week band have been attributed to baroclinic topographic Rossby waves, but with just two widely spaced moorings, we cannot infer the wave number and test for such waves using the dispersion relationship. However, an indirect estimate of wave number can be made by examining the variation of spectral power with depth, and doing this yields results that are reasonably consistent with a linear theory of baroclinic topographic Rossby waves for water of constant stratification over a planar slope. This agreement is somewhat surprising, given the simplicity of the theory and the complexity of the domain, but it appears to offer a clear indication of the importance of baroclinic vorticity dynamics in this region.